1. Field of the Invention
The present invention relates to a method and an apparatus for pattern recognition capable of recognizing a given pattern by means of evaluating a quantity called a multiple similarity.
2. Description of the Background Art
A method for pattern recognition called the multiple similarity method has been known, the detail of which is disclosed by Iijima et al. in U.S. Pat. No. 3,688,267 and by Maeda in U.S. Pat. No. 4,503,557. In this multiple similarity method, a quantity called a multiple similarity defined as: ##EQU1## where i is an integer, R.sub.i are n-orthogonal vectors determined from the standard patterns, V is a density pattern vector for an input pattern indicating a distribution of segments that constitute the input pattern, k.sub.i are coefficients, and (,) designates an inner product, is evaluated so that inessential difference between the input pattern and the standard pattern such as positional displacement can be ignored. As a result, it is possible in the multiple similarity method to achieve a highly accurate pattern recognition.
However, when a pattern to be recognized may involve complicated and diverse variations such as in a case of a hand written letter, it has not been possible to achieve a sufficient recognition accuracy even with the multiple similarity method. This is due to the fact that in the multiple similarity method the ability of recognition relies on density patterns of the input pattern, and not on a structural feature of the input pattern.
The density pattern in the multiple similarity method indicates the distribution of segments that constitute the input pattern, which is obtained by detecting a number of black picture elements that make up segments of the pattern, as oppose to the white picture elements that make up the background, within each one of regions which subdivide the input pattern, and by constructing a density pattern vector which indicates these number of black picture elements in different regions. Thus, for example, a pattern "#" may not be distinguished from a pattern "+" written in bold, as a number of black picture elements in a boldly written single line and that in double lines may not differ substantially.
It has therefore not been possible in a conventional pattern recognition method to achieve a satisfactory recognition accuracy when a pattern to be recognized may involve complicated and diverse variations such as in a case of a hand written letter, as structural features of a pattern to be recognized are not taken into account.